Lithium greases containing excess lithium hydroxide



United States P lj LITHIUM GREASES CONTAINING EXCESS LITHIUM HYDROXIDE Lcrne W. Sproule, Sarnia, Ontario, Laurence F. King,

Mooretown, Ontario, and Warren C. Pattenden, Courtright, Ontario, Canada, assignors to Esse Research and Engineering Company, a corporation cf Delaware Application March 22, 1956, Serial No. 573,123

2 Claims. (Cl. 25242.1

The present invention relates to improved greases and methods for their preparation. More particularly, the invention pertans to improved lithium gr eases and their manufacture.

This application is a continuation-in-part cf Serial No.

315,056, filed October 16, 1952, and now abandoned, having the same inventorship.

In its broadest aspect, the invention is concerned with lubrcating greases containng as a grease thickenet the lithium soap cf hydroxy stearic acid, and a small propor:

tien cf excess lithium hydroxide. Greases of this type are superior to similar greases free of excess.lithium hydroxide, with respect to their stabilitv at high tempera turcs and high speeds of the frictional surfaces lubricated.

Lithium 'greases have been known and widely usedfcr severl years. The lithium soaps Used as the thickeher for these greasesis usuallyprepad by reacting lithium hydroxide or other suitable lithium bases in substantiafly stcichiometric proportions with conventional high molecular weight acids. These lithium scaps may be incorpcrated in suitable minerai or synthetc lubricating cils in proportions varying between about 1 and 20 wt. percent, depending on the consistency of the grease desred.

Lithium greases of this type have the unique characteristie of combining high dropping point with high water resistance and case of dispersion in all types of lubricating cil. These prope1ties have made lithium greases particularly valuable for many aeronautcal and military applications. However, the utility cf these greases is some what curtailed by their relatively short lubricating lite, particularly at high temperatures and high frictional speeds. Conventional ant-oxidants, such as, for example, phenyl-alpha-naphthylamne, are not very effective in prolonging the lubricating life of these greases.

The present invention overcomes this drawback and alords various additional advantages as will appear more clearly from the. subsequent description of the invention and the practical examples given, wherein reference will be made to the accompanying drawing the single figure of which is a graphical illustration cf beneficial eiects aiorded by the invention.

It has now been found that the lubricating life et lithium hydroxy stearate thickened greases may be substantially extended by incorporating into the grease an appreciable free alkalinity in the form of excess lithium hydroxide over that required to neutralize the fatty acid. The excess cf lithium hydroxide should amount to at least about 1.0 wt. percent and may be as much as 2 wt. percent or more, based on the finished grease. However, concentrations above about 1.5 wt. percent are only slightly more effective than lower concentrations within this range. The preferred range of excess lithium hydroxide is, therefore, about 1.0 to 1.5 wt. percent. It is essential for the purposes of the invention that the free alkalinity of the fin ished grease results predominantly from the presence of excess lithium hydroxide as distinguished from other basic lithium compounds, such as the carbonate which has been found to be rather inefiective.

ingoils may also be efiectively utilized. The grease com positions of the invention Will usually contan about,70 t0 95, preferably about 80 to 92, wt. percent, based on the preferably about 8 to 20, wt. percent, based on the total grease, of the lithium soap cf 12-hydrcxy stearic acid may be employed in preparing the lubricating grease compositions et the invention. in general, any of the conven: tronal lubrrcatmg cils such as mineral, animal, vegetable and synthetic lubricating cils, may be employed as the grease base. These lubricating cils will have a viscosity:

of about 35 to 200 SSU at210 F. Mixtures cf lubricattotal grease, of the lubricating cil base.

' Greases in accordance withthe invention may be prepared as follows. The hydroxy stearic acid may be dissolved in lubricating cil Whle heating to about 125 -175 F. at atmospheric pressure. Lithium hydrcxide is added to this solution in amount sufficient for complete neutraL nation of the hydroxy stearic'acid and to provide the adesired excess cf lithium hydroxide in the finished g'rease.

The mixture may then be dehydrated by heating -to about,

280"320 F.. at atmospheric pressure. Thereafter the grease may be diluted with additional lubricating oil and melted at temperatures usually above 400 F. at atmos- The gr'ease ma then be cooled with mill.

The invention will be further illustrated by the follow 1 ng specific example which is not intended to be limiting m scope.

A number of greases were prepared as hereinafter described, and tested for their lubrication life by the standard spindle lite test #33.1 of Federal Specificafion V.V.L. 791D at 250 F. and a bearing rotating speed cf 10,000 r.p.m. Excess lithium hydrcxide was determined by titrating the grease dispersed in 50 parts petroleum ether and 50 parts ethyl alcohcl at room temperature. Total alkali which includes lithium hydroxide and lithium carbonate was determined by adding 10 ml. cf standard hydrochlorc acid, refluxing and back-titrating.

EXAMPLE Grease A.This grease was prepared by reacting the hydroxy stearic acid dissolved at F. in an equal weight of the minerai lubricating cil, having a viscosity cf 60 SSU at 210 F. and a viscosity index of 50, with an aquecus solution cf lithium hydroxide. After dehydrating the mixture at 300 F., the balance of the oil was added and the grease was melted at 410 F. The molten grease was then stirred down in a grease mixer, the phenyl alpha-naphthylamine added and, when ocld, passed thrcugh a grease mill. The final grease composition did not contain any free lithium hydrcxide, but it did ccntain 0.04% lithium carbonate as excess alkali.

Grease B.This grease was prepared in the manner described in the preparaon cf grease A, with the exceptien that sufficient aquecus lithium hydroxide was added to ccmpletely neutralize the hydroxy stearic acid and to provide an excess of about 0.52% free lithium hydroxide.

Grease C.This grease was also prepared in the manner described in the preparatcn cf grease A, with the exception that sufiicient aquecus lithium hydroxide was added to provide an excess of about 1.08% froc lithium hydroxide and 0.02% lithium carbonate.

Grease D.-This grease was prepared by reacting the stearic acid dissolved at 150 F. in an equal weight of a mineral lubricafing cil having a viscosity cf 66 SSU at e ate r: .1952:

210 F. and a visdit indei of 90, With an aqueous solution of lithium hydroxide. Suflicient aqueous lithium hydroxide was used to completely neutralize the stearic acid and to provide an eXces s of about 1.08% free lithium hydroxide. After dehydrating' the mixture at 300 F., the balance of the oil was added, and the resulting grease mlted at 410 F. The molten grase was then cast into pans, allowed to cool to room temperature and then homogenized in a grease mixer. About 1 wt. percent of phenyl alpha-naphthylamine was added prior to casting the grease.

The formulations and inspections of greases A to D are tabulated below:

Table 1 Gr'ease'Desigmtion A B C D Formula, percent by Weight:

Stearlc Avir 7 12.0 12 Hydroxy-Staaric Acld 9. 5 9. 5 9 5 Lithium Hydroxlde Monohydrate l. 4 l. 9 2. 4 3.0 Mineral 0i1 (Vise. 210 F., 60 V.I.

.50) 88. 1 87. 6 87. 1 (Vise. 210 F., 66 V.I. 8 0 Phenyl alpha nsphthylamine.-.. 1.0 1.0 1.0 1.0 Inapectlons:

Percent Excess Lithium Hydroxide.. Ni] 0. 52 l. 08 l. 08 Percent Total Excess Allmlr- O. 04 O. 60 1. 10 1. 10 Worked P fl tmfi 244 300 270 Spindle 'Llfe 250 F.'hrs l, 133 1, 174 2, 200 909 V Th flt of varying concentration of free lithium be'rioted that the upwid"slope of the spindle lifecurv increases rapidly at a free lithium hydroxide concentratiOn above about 1.0%.

The above data show that lithium l2-hydroxy stearate thickened greases having a free lithium hydroxide content of at least about 1.0 wt. percent have a considerably higher lubricating lite (grease C, 2200 heurs) than similar greases having no excess lithium hydroxide (grease A, 1133 hUIS) or a free lithium hydroxide content of less than 1.0% (grease B, 1174 heurs). In addition, the data *further show that the lubn'cating life of grease C, the inventive grease composition, was also considerably higher than the lubricating life of a lithium stearate thickened grease containing the same amount of free lithium hydroxide (grease D).

It is to be understood that conventional additives may be used in the grease composition of this invention. These additive materials, such as tackiness agents, viscosity index improvers, anti-corrosion agents, oxidaon inhibitdis, xtrenie pressure agents, etc., may be incorporated by methods familiar to the art.

What is claimed is:

1. A lubricating grease composition comprising a major proportion-cf a mineral lubricating oil, a minor grease mking proportion of a lithium soap of hydroxy stearic acid and in the range of 1.0 to 2.0 wt. percent free lithium hydroxide.

2. The lubricating grease composition of claim 1 wherein sad hydroxy stearic acid is 12hydroxy stearic acid.

References Cited in the file of this patent UNITED S'iAlES PATENTS 

1. A LUBRICATING GREASE COMPOSITION COMPRISING A MAJOR PROPORTION OF A MINERAL LUBRICATING OIL, A MINOR GREASEMAKING PROPORTION OF A LITHIUM SOAP PF HYDROXY STEARIC ACID AND IN THE RANGE OF 1.0 TO 2.0 WT. PERCENT FREE LITHIUM HYDROXIDE. 